Not easily.
A possibility that is quite dirty: CircleOS allows to modify the irq vectors. You could use an unused irq for this purpose. But you need to be sure that no other application will use this irq.
Another possibility (cleaner): you can see how CircleOS looks for the test application in the FAT (see CircleOS, menu_settings.c, line 734). CircleOS calls Fct_Init(), but it could call another function if you build an array of pointers to functions in the startup file.